1. Field of the Invention
The present invention refers to a voltage multiplier and to the relative operating method.
2. Description of the Related Art
The tendency to decrease the supply voltage of the integrated devices placed in electronic equipments, such as telecommunication equipments, portable computers, etc., requires the presence in said equipments of circuit blocks, commonly called boosters, capable of raising the supply voltage in input. The use of a minor number of components is often required to produce said booster and high efficiency of conversion of the supply voltage to a higher one is often requested.
For this object the charge pump cells are used as boosters because of the fact that the components they are formed of are readily available in the same integrated circuits.
A voltage booster that uses charge pump cells is described in the U.S. Pat. No. 5,874,850. The booster comprises an oscillator suitable for generating two signals in phase opposition and an accumulation capacitor connected between the output of the booster and ground. The booster comprises at least one charging section comprising an output terminal coupled to the output terminal of the booster, an input terminal coupled with a constant input voltage and a first side terminal and a second side terminal connected respectively to the outputs of the oscillator. The at least one charging section comprises a first capacitor and a second capacitor having first terminals connected with the side terminals and a bridge of four MOS transistors suitable for charging alternately said two capacitors in respective charging periods; said bridge has intermediate terminals connected to the second terminals of the capacitors, one terminal connected to the input terminal of the charging section and another terminal connected to the output terminal of the charging section.
The charge transfer capacitors each have a parasitic capacitance placed between one of their terminals and ground; these parasitic capacitances are the main cause for the efficiency loss of the booster which is due to the current that flows through the parasitic capacitances. The value of this current depends on the supply voltage, on the switching frequency of the transistors and above all on the value of the parasitic capacitances; the higher the value of the parasitic capacitances in relation to the charge transfer capacitors, the greater the value of the current and the higher the power consumption.